A major objective of the proposed investigation will be to document the timing, distribution and nature of histological and ultrastructural changes exhibited by the mesenchymal and epithelial cells during prenatal development of the cranio-facal region in the oel genetic mutant mouse. Two recessive genes of interest are expressed in this stock: oel which produced congenital clefts of the secondary palate and open eyelids; and crn which produces congenital cranioschisis but no cleft palate. Cells will be examined from day 8 to birth by light microscopy, transmission electron microscopy and scanning electron microscopy. Mitotic activity will be assessed by tritiated thymidine labelling and autoradiography. Cell membrane structure will be examined by freeze-fracture techniques. These studies will provide essential morphological data as a prelude to future biochemial and immunological studies.